The present invention relates generally to gas turbine engines, and, more specifically, to combustors therein.
A typical gas turbine engine includes a multistage compressor for pressurizing air which is mixed with fuel in a combustor for generating hot combustion gases. The gases flow through a high pressure turbine (HPT) which extracts energy for powering the compressor. A low pressure turbine (LPT) extracts additional energy for providing output work, such as powering a fan in a turbofan aircraft engine application, or providing output shaft power in land-based or marine applications.
In designing a turbine engine for powering a military vehicle, such as a main battle tank, the size and weight of the engine must be as small as possible, which correspondingly increases the difficulty of integrating the various engine components for maximizing performance, efficiency, and life. For example, one engine being developed includes an exhaust heat exchanger or recuperator which uses the hot combustion gases discharged from the turbines for additionally heating the pressurized air discharged from the compressor for increasing engine efficiency. However, this hot pressurized air must also be used for cooling the combustor components themselves which further increases the complexity of the combustor design.
In the last two decades, a double-wall combustor design underwent considerable development effort which did not lead to commercial production thereof. Radially outer and inner combustion liners were supported from corresponding radially outer and inner annular supports. Compressor discharge air was channeled through apertures in the supports for impingement cooling the outer surfaces of the liners. The spent impingement air was then channeled through film cooling and dilution holes in the liners for cooling the liners themselves, as well as providing dilution air for the combustion gases generated in the annular combustion chamber.
A consequence of the double wall combustor design is the inherent difference in operating temperature between the liners and the surrounding supports. Differential operating temperatures result in differential thermal expansion and contraction of the combustor components. Such differential thermal movement occurs both axially and radially, as well as during steady state or static operation and during transient operation of the engine as power is increased and decreased.
The liners must therefore be suitably mounted to their supports for accommodating differential thermal movement therebetween, while also minimizing undesirable leakage of the pressurized air coolant. The liners must be mounted concentrically with each other and with the supports to minimize undesirable variations in temperature distribution, both radially and circumferentially around the outlet end of the combustor as represented by the conventionally known pattern and profile factors.
Liner alignment or concentricity with the turbine is therefore an important design objective for an annular combustor, and is rendered particularly more difficult due to the double-wall liner configuration. Liner alignment affects all aspects of the combustor performance including cooling thereof, dilution of the combustion gases, and turbine performance. And, liner mounting to the supports must minimize thermally induced stress therein for ensuring maximum life of the combustor during operation.
The development combustor disclosed above was designed for proof-of-concept and lacked production features for the intended service life requirements in the tank application. For example, studs were welded to the outer liner and simply bolted to the outer support for mounting the outer liner thereto. In turn, the entire combustor was aft-mounted to a support casing through the outer combustor wall. This bolted design inherently fails to accommodate differential thermal movement between the liner and outer support and results in considerable thermal stresses during operation.
Accordingly, it is desired to provide an improved double-wall combustor design for accommodating differential thermal movement during operation while maintaining concentricity of liner support.